Fine drill head with slack-free radial displacement

ABSTRACT

The invention relates to a tool head, especially a fine drill head, comprising a machine shank and a tool shank having a joint center axis, wherein the tool shank has a rigid core and a head with a tool, supported by a parallel spring arrangement and is able to be elastically displaced in relation thereto, said head having several limbs which emanate therefrom and form the parallel spring arrangement, whereby at least one of said limbs is fixed to the core or machine shank. The inventive tool head also comprises a device for radial displacement of the head in relation to the core, comprising a positioning device which has a conical part and is guided inside the core. The conical part bears against a contact part of the parallel spring arrangement under pressure when in use. The core is configured with the parallel spring arrangement in a single piece.

PRIORITY CLAIM

This is a U.S. national stage of application No. PCT/DE02/00546, filedon 15 Feb. 2002. Priority is claimed on that application and on thefollowing application(s): Country: Germany, Application No.: 101 08794.2, Filed: 15 Feb. 2001.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a tool head, in particular a precision boringhead, having a machine shank and a tool shank which have a commonmid-axis, the tool shank having a core and a head which is borne by aparallel spring arrangement that can be deflected resiliently inrelation thereto and has a tool, in particular a head with a pluralityof legs which originate from said head and form a parallel springarrangement, of which at least one leg is fixed to the core or machineshank, and to a device for the radial adjustment of the head relative tothe core.

2. Description of the Prior Art

A boring head of the generic type is disclosed by DE 33 32 243 A1. Inthis boring head, a spring-loaded, long pin with a head in the shape ofa truncated cone is guided in the axial direction in its tool shank andcan be adjusted in the axial direction. By means of axial displacementof the truncated cone-shaped pin which, for its part, presses against abolt arranged in the head of the parallel spring arrangement, the toolin the head has impressed on it a slight radial movement correspondingto the pitch of the conical surface, and thus the tool is adjustedradially outward or inward. This device has been tried and tested inpractice, but the tool head is relatively long and the tool-cutterholder is fixed in its position only by surface friction. In addition,this tool has very many parts and is therefore relatively expensive, andthe tool must be implemented in cooperation with the machinemanufacturer, because of the adjusting device being driven by signalsfrom the machine. A further disadvantage resides in the fact that,because of the design, the coolant flows through the adjustment regionof the setting device and therefore the setting device cannot always beset under the same conditions, because of contamination by coolant.

DE 39 26 026 A1 discloses a tool head of similar type, in which aparallel spring arrangement can be deflected resiliently against a basebody. The tool is held in the parallel spring arrangement and can beadjusted radially by means of a device comprising a setting screw with aconical part, which bears with prestress against a complementary surfaceon the parallel spring arrangement. The disadvantage is that this devicecan be used only for a specific tool design, a long chisel, since, withthis chisel, at the same time an imbalance compensating device isintended to be actuated in reverse, in order that highly accurate boringcan be achieved with tools of this type. A further disadvantage consistsin the fact that the tool cannot be preset and coolant flows through thesetting region in which the setting screw is located, and through theimbalance compensating device.

SUMMARY OF THE INVENTION

On this basis, the invention is based on the problem of avoiding thedisadvantages of the prior art, but using its advantages, of being smallwith few device parts and of arranging these parts in such a way thatspace remains for leading the coolant duct through as far as the tool.The intention is for minimal, radial setting to be possible undercontrol with exact fixing of the setting position. Further problemsassociated with the use of a tool head of this type, which the inventiondeals with, emerge from the respective explanation of the solutionindicated.

The first solution in the case of the generic tool head is to form thecore and the parallel spring arrangement together in one piece. Thenecessary division of the parallel spring arrangement from the core canbe carried out by methods which are familiar nowadays, by means ofdrillings and erosion tools which are to be used in order to produce anarrow groove for the mobility of the parallel spring on the core. Thisarrangement is conceived in particular for tools of small diameter, inwhich extremely precise adjustments in the radial direction is required.In the case of the tool according to the invention, the adjustment canbe carried out in the range of 1 μm in the radial direction, that is tosay 2 μm bore diameter. In a particularly preferred embodiment, the headfor holding the cutter holder or the tool holder is also arranged in onepiece with the parallel spring, so that neither play nor undesiredmispositioning of the head on the parallel spring arrangement can occur.

A second solution of the problem according to the invention provides forthe contact part to be a positionable, presettable screw with an arm ofthe parallel spring arrangement, the arm extending back from the head inthe direction of the machine head and, on the opposite side, in thecore, for the setting device to be screwed into the core, transverselywith respect to the mid-axis, as a setting screw. An extremely compacttool is therefore made possible, which the edges of the parallel springarrangement did not permit the hitherto, since they were arranged in aseparate part of the spring.

As is known per se, the setting screw is provided with a conical surfaceor a conical part which bears under prestress on an opposing part, anabutment according to the prior art or, according to the invention on aspecifically formed pressure screw having an end face that is compatiblewith the conical part.

A tool shank formed in this way still leaves space for a coolant borewhich, in the core, is led past the setting device, penetrates the slotand ends in the parallel spring arrangement on the head, the necessaryslot between parallel spring arrangement and core being overcome by ahose. Instead of a hose, a similarly flexible element can also be used.

In one embodiment, the cutter holder is formed in such a way that it isarranged in a clamping groove in the tool head, transversely withrespect to the mid-axis of the entire tool, so that it is radiallyadjustable. The cutter holder, which, for example, is provided with areversible cutting plate, is preferably fixed in at least two axes byappropriate pressure screws. In a preferred embodiment, one of thescrews is formed in such a way that it can fix the cutter holder in twoaxes, specifically in order to absorb forces in the horizontal and axialdirection, in that an oblique depression is introduced into the cutterholder, onto which one of the pressure screws is placed and, with anappropriate pressing force, fixes the cutter holder in two axes.

Instead of a cutter holder of this type, provision can also be made fora different cutter holder, for example a long chisel, as known from theprior art, to be fitted to the end face of the head of the tool shank bymeans of a screw fitting. In this case, the rear face of the cutterholder and the end face are preferably designed to be flat and thecutter holder with the head is screwed firmly by means of a union nutonto the head, which has a thread corresponding thereto. This results ina play-free connection. The cutter holder preferably also has a coolantbore and, via the clamping groove, which in this case is not used, issupplied by the cooling liquid line in the core with generosity, whichcan then pass through the cutter holder to the tool tip in the bore, inorder to provide liquid emerging at the connecting point in the unionnut, which is either integrally molded in one piece on the cutter holderor, as a true union nut, engages around the cutter holder and the headat the tool shank, with the appropriate seals, which are compressed bythe union nut being screwed on and therefore hold tightly. Such a designof the cutter holder is suitable in particular for small bores which areadditionally deep and, in addition, if only one tool head of the typeaccording to the invention is used, a wide range of bores, starting fromabout 5 mm up to 70 or 80 mm, can be produced. In a special case, thecutter holder itself can also be formed as a borer in order to producesmall bores. In this case, however, no radial adjustment is required ifthe borer is formed as a double cutter.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is to be explained in more detail by using the drawing ofan exemplary embodiment, in which:

FIG. 1 is an exploded perspective view of the tool head according to theinvention;

FIG. 2 is a perspective view of the tool head according to the inventionfollowing assembly;

FIG. 3 is a side view of the tool head according to FIG. 2 with adotted-line representation of the parallel spring arrangement;

FIG. 4 is a section through the setting device according to theinvention according to the section position IV—IV in FIG. 3;

FIG. 5 is an embodiment of the tool shank on its own analogous to FIG.1; and

FIG. 6 is a side view of a further embodiment of a tool shank.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

The drawing shows, partly schematically, a tool, approximately at theoriginal size, for boring out or precision boring a hole with a diameterof about 35 mm. This is only an exemplary embodiment. The practicaldiameter for tool heads of this size also permits diameters from about10 mm, in particular if a long chisel is used.

FIG. 1 shows an exploded illustration of the substantial parts of thetool head or the elements to be assembled on a tool shank, for exampleaccording to FIG. 5, and the assembled state of the tool head accordingto FIG. 1 in FIG. 2. The tool head has a machine shank 1 with anydesired holder for a spindle of a machine tool and is provided, forexample, with a conventional annular collar 2 for the attachment of aclamping tool (not illustrated) for the tool head in the machine. Thetool shank, designated generally by reference number 3, comprises a core10 (FIG. 5) and a parallel spring arrangement 11 to accommodate a toolholder, 4. In the embodiment of FIG. 1, the tool holder 4 comprises acutter holder 14, on which, by means of fixing screw 19, a commerciallyavailable reversible cutting plate 18 can be fixed. The tool holderfurther comprises a head 20 with an end face 21 to hold a cutter holder14, which can slide in a guide groove 22 and can be fixed in itsposition. This fixing is provided by means of a screw 17, which isintroduced into a threaded hole 171 in the head 20 in such a way that,by using the screw 17, pressure can be exerted on that side 142 of thecutter holder 14 which lies opposite the reversible cutting plate 18. Inthe other axis, orthogonal thereto, the cutter holder 14 is held by apressure piece 15 by means of clamping screw 16, which can both beinserted through threaded hole 151, the pressure piece 15 coming to bearon the oblique face 141 in the cutter holder 14. By means of the shapingof the depressed face 141, inclined with respect to the surface of thecutter holder 14, the cutter holder is fixed in its position both in thedirection of the mid-axis X (FIG. 3) and in a horizontal direction,while it can be positioned in the second horizontal direction by thepressure screw 17 bearing on contact point 142. The cutter holder ispre-positioned for the corresponding diameter with the aid of theoutlined pressure screws 16 and 17. The part 20 is the head of theparallel spring arrangement 11, which has spring legs 113, 114 (see FIG.5), which are connected firmly to the head 20 but permit a resilientradial adjustment of the head 20. For radial adjustment, use is made ofa setting device which is arranged between the core 10 and the parallelspring arrangement 11 and is primarily formed of a setting screw 100(FIG. 4), which has a conical part 101 and a threaded part 102, whichcan be screwed by means of a tool which is not illustrated but can beinserted into hole 103. On its top face, the screw is provided with amarking 104 which can be read off against a notch 107 arranged on thecore 10. The screw 100 is situated in a sleeve 108 fixed in the core 10and having an internal thread, and in this way can be adjustedtransversely with respect to the mid-axis X of the tool head. In thiscase, the conical part 101 of the screw acts on the actuating face 201of a screw 200, which is inserted into the abutment part 110 of the head20, springing back in the direction of the machine shank 1 in the mannerof a stiff carrier, so that it can make contact with the screw 100. Inorder to insert the screw 200, the leg 114 has a hole 115 for the screw200 to pass through. The screw 200 can be pre-positioned for a specificdiameter range to be produced.

In this way, the parallel spring arrangement is imparted a prestress,that is to say it is forced out of the stress-free neutral springposition, and supplied in this way from the factory. The purpose is topermit no change in the diameter when cutting inserts such as cuttingplates are used, in which the reaction forces on the cutter to thecutting forces leads to the cutter being “pulled” into the workpiece andtherefore the bore becoming larger and impermissibly exceedingtolerances. If the bore which is to be produced with the tool head is tobecome slightly smaller or larger, then the screw 100 can be screwedmore deeply or less deeply into the sleeve 108 and, in the process,forces the outer parallel spring parts to undergo a position change. Thescrew 200 is seated in an abutment 110 which originates from the head20, is of cantilevered design and belongs to the parallel springarrangement 11, and which has a cross-section which is larger than thecross section of the leg parts 113, 114 and itself therefore virtuallydoes not bend resiliently but, with appropriate pressure on the screw200, deflects the parallel spring and therefore the tool outward. As aresult of arranging the conical face 101 on the setting screw 100, fineoutward deflection of the parallel spring is thus possible, in the rangeof an adjustment in radial steps of 1 μm. Therefore, current accuracyrequirements on the bores are satisfied in virtually all cases.

By using a dust cap 13 which, by means of screw 131, can be screwedthrough a hole 133 in the dust cap 13 into the thread 132 on the head20, dirt is prevented from getting into the setting area or the regionof movement of the parallel spring and impairing the setting of theparallel spring.

In addition, in relation to the machine shank 1 or annular collar 2 in,the tool head 3 is provided in with two or more balancing rings 24, 25which, in order to compensate for the unequally distributed masses onthe tool head, are themselves provided with a recess (not illustrated),which can be positioned in such a way that the imbalance of the toolhead is minimized. Following the correct setting, with the aid of ascrew through the hole 241, the rings are fixed in their position in aclamping groove 242 on the core 10 or the annular collar 2 (FIG. 3).This tool, equipped in this way, can be operated with extremely highrotational speeds up to about 30 000 revolutions per minute and produceextremely finely toleranced bores.

FIG. 5 shows a tool shank in which the core 10 is formed in one piecewith the parallel spring 11. According to FIG. 1, the tool shank 3 isconnected to the machine shank 1 or the annular collar by a threadedconnection. In FIG. 5, the head 20, which in one embodiment could bescrewed on to the parallel spring, is likewise illustrated as a part inone piece with the parallel spring 11. This enlarged situation shows, ina virtually identical design to FIG. 1, that the abutment 110 isarranged overall as an arm springing back toward the machine shank 1 andbelonging to the head 20 and therefore the parallel spring 11, and has athreaded hole 210 into which, through an aligned hole 115 in the leg 114of the parallel spring arrangement 11, the screw 200 (FIGS. 1, 4) can beinserted, meeting a setting screw 100 (FIG. 4) arranged in the threadedhole 109. The groove 119 separates both the legs 113, 114 and theabutment 110 from the core 10, and also the coolant feed 12 in the core10 from the extension of the coolant bore 12 in the parallel springarrangement, which has an outlet 121 in the head just underneath thetool, to cool the same. The gap in the coolant line is closed by aflexible line, for example a hose, which is not shown, in order that thecoolant can pass unimpeded as far as the head or the working tool.

The tool shank with head 20 illustrated in FIG. 5 is shown without atool holder with a tool, for example a reversible cutting plate 18.Instead of receiving tool holder 14, the head 20 may be provided on thecollar 26 with a thread, as shown in FIG. 6 which is designed to becomplementary to a union nut 226 (shown schematically in FIG. 6). Theunion nut 226 is preferably coupled in one piece to a cutter holder (notillustrated) which can be placed flat on the front side 21 of the head20 and at whose tip or outermost end a tool cutting plate can belocated. Using such a chisel arrangement, very deep and small bores canbe machined. The setting for bores to be toleranced in a correspondingway can, as explained, be made with the screw 200 or setting device 100,as has also been explained using the example of the tool holder 14. Thecutter holder of this alternative embodiment may be hollow in order tolead coolant through. The coolant feed 12, coming from the shank, endson the head 20 in the clamping groove 22, which has no function here andis provided in the union nut 226 with a seal in relation to the head 20.As a result, through the cooling liquid bore 12 and via the clampinggroove 22, it is possible to bring coolant into the cutter holder—notillustrated—which extends toward the workpiece approximately on themid-axis X. The seal 26 a can be formed as an O ring, the nut relatingto the head or the union nut can be formed as a separate part or else bearranged on the cutter holder. For this purpose, the cutter holderitself is screwed with its rear end flat on the end face 21 of the head20, so that it has appropriate guidance on the end face 21 and, at thesame time, presses the sealing rings, and thus cooling liquid can passunimpeded to the cutter holder.

1. A tool head for precision boring, comprising: a machine shank; a toolshank connected to the machine shank and having a common longitudinalaxis therewith, said tool shank including a core, a parallel springarrangement resiliently deflectable relative to said core, and a headconnected to said core by said parallel spring arrangement, wherein saidparallel spring arrangement includes a plurality of legs originatingfrom said head, at least one of said plural legs being connected to oneof said core and said machine shank, said core being formed as one piecewith said parallel spring arrangement; and a device for radialadjustment of said head relative to said core comprising a settingdevice having a conical portion which bears under a prestress generatedby said parallel spring arrangement on a contact portion of saidparallel spring arrangement, wherein said contact portion comprises anarm of said parallel spring arrangement with a presettable screwarranged in said arm, said arm extending toward said machine shank, saidsetting device being threadably inserted into said core transverse tosaid longitudinal axis of said core.
 2. The tool head of claim 1,wherein said presettable screw comprises an end face forming a contactpairing with said conical part of said setting device.
 3. The tool headof claim 1, wherein said setting device comprises a head having anoutward facing visible portion including a marking to indicate itsrotary position relative to said core.
 4. A tool head for precisionboring, comprising: a machine shank; a tool shank connected to themachine shank and having a common longitudinal axis therewith, said toolshank including a core, a parallel spring arrangement resilientlydeflectable relative to said core, and a head connected to said core bysaid parallel spring arrangement, wherein said parallel springarrangement includes a plurality of legs originating from said head, atleast one of said plural legs being connected to one of said core andsaid machine shank, said core being formed as one piece with saidparallel spring arrangement, and wherein said head comprises an externalthread for threadably receiving a union nut for holding a cutter holder;and a device for radial adjustment of said head relative to said corecomprising a setting device having a conical portion which bears under aprestress generated by said parallel spring arrangement on a contactportion of said parallel spring arrangement.
 5. The tool head of claim4, wherein said parallel spring arrangement is formed as one piece withsaid head.
 6. The tool head of claim 4, wherein a position of saidconical portion of said setting device bearing against said contactportion is adjustable for effecting radial adjustment of said headrelative to said core.
 7. The tool head of claim 4, further comprising acooling duct in said core connected to a further cooling duct in saidhead.
 8. The tool head of claim 4, further comprising a tool holderreceivable in a groove in said head and pressure screws for at leasttwo-axis fixing of said tool holder in said groove.
 9. The tool head ofclaim 4, further comprising a seal for preventing coolant from exiting acooling duct in said head.
 10. A tool head for precision boring,comprising: a machine shank; a tool shank connected to the machine shankand having a common longitudinal axis therewith, said tool shankincluding a core, a parallel spring arrangement resiliently deflectablerelative to said core, and a head connected to said core by saidparallel spring arrangement, wherein said parallel spring arrangementincludes a plurality of legs originating from said head, at least one ofsaid plural legs being connected to one of said core and said machineshank; and a device for radial adjustment of said head relative to saidcore comprising a setting device having a conical portion which bearsunder a prestress generated by said parallel spring arrangement on acontact portion of said parallel spring arrangement, said contactportion comprising an arm of said parallel spring arrangement with apresettable screw arranged in said arm, said arm extending toward saidmachine shank, said setting device being threadably inserted into saidcore transverse to said longitudinal axis of said core.
 11. The toolhead of claim 10, wherein said presettable screw comprises an end faceforming a contact pairing with said conical part of said setting device.12. The tool head of claim 10, wherein said setting device comprises ahead having an outward facing visible portion including a marking toindicate its rotary position relative to said core.
 13. The tool head ofclaim 10, further comprising a cooling duct in said core connected to afurther cooling duct in said head.
 14. The tool head of claim 10,further comprising a tool holder receivable in a groove in said head andpressure screws for at least two-axis fixing of said tool holder in saidgroove.
 15. The tool head of claim 10, wherein said head comprises anexternal thread for threadably receiving a union nut for holding acutter holder.
 16. The tool head of claim 15, further comprising a sealfor preventing coolant from exiting a cooling duct in said head.